CSI feedback design for new radio

ABSTRACT

It is recognized herein that as the number of transmit antennas in cellular systems (e.g., NR or 5G systems) increase, the Channel State information (CSI) feedback overhead may increase to unacceptable levels, and the current CSI feedback might not support beamforming training for NR. Embodiments described herein provide an enhanced and more efficient design for Channel State Information feedback as compared to current approaches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/373,645, filed Aug. 11, 2016, the disclosureof which is incorporated by reference in its entirety.

BACKGROUND

In Long Term Evolution (LTE), multi-antenna techniques are used toachieve improved system performance, which may include improved systemcapacity (e.g., more users per cell), improved coverage (e.g., largercells), and improved service provisioning (e.g., higher per-user datarates). The availability of multiple antennas at the transmitter and/orthe receiver can be utilized in different ways to achieve differentobjectives, such as, for example, objectives related to antennadiversity, antenna beamforming, and antenna spatial multiplexing. Forexample, multiple antennas at the transmitter and/or the receiver can beused to provide antenna diversity against fading on the radio channel.Multiple antennas at the transmitter and/or the receiver can be used to“shape” the overall antenna beam in a certain way, which can be referredto as antenna beamforming. For example, antenna beamforming can be usedto maximize the overall antenna gain in the direction of the targetreceiver or to suppress specific dominant interfering signals. Multipleantennas can be used for antenna spatial multiplexing, which refers tothe simultaneous availability of multiple antennas at the transmitterand receiver to be used to create multiple parallel communication“channels” over the radio interface. Antenna spatial multiplexing canprovide high data rates within a limited bandwidth, which is referred toas Multiple-Input and Multiple-Output (MIMO) antenna processing.

Turning now to downlink (DL) reference signals in LTE, DL referencesignals (RSs) are predefined signals occupying specific resourceelements (REs) within the downlink time-frequency RE grid. LTE definesseveral types of DL RSs that are transmitted in different ways fordifferent purposes. For example, a cell-specific reference signal (CRS)can be used: (1) by terminals (UEs) for channel estimation for coherentdemodulation of DL physical channels; (2) by UEs to acquire ChannelState Information (CSI); or (3) by UEs as the basis for measurement ofcell-selection and handover. DeModulation Reference Signals (DM-RSs) areanother example of a DL RS. A DM-RS can be referred to as User Equipment(UE)-specific reference signals that are intended to be used by UEs forchannel estimation for coherent demodulation of DL channels. DM-RSs maybe used for channel estimation by a specific UE, and then transmittedwithin the RBs specifically assigned for PDSCH/EPDCCH transmission tothat UE. DM-RSs are associated with data signals and precoded prior tothe transmission with the same precoder as data. Channel StateInformation Reference Signals (CSI-RSs) are another example of a DL RS.CSE-RSIs are intended to be used by UEs to acquire CSI forchannel-dependent scheduling, link adaptation, and multi-antennatransmissions.

Turning now to uplink reference signals, similar to LTE DL, referencesignals are also used in LTE UpLink (UL). LTE defines UL DemodulationReference Signals (DM-RSs) and UL Sounding Reference Signals (SRSs). ULDemodulation Reference Signals (DM-RSs) are used by the base station forchannel estimation for coherent demodulation of the Physical UplinkShared CHannel (PUSCH) and the Physical Uplink Control CHannel (PUCCH).In LTE, DM-RS are only transmitted within the RBs specifically assignedfor PUSCH/PUCCH transmission and span the same frequency range as thecorresponding physical channel. UL Sounding Reference Signals (SRS) areused by the base station for CSI estimation for supporting uplinkchannel-dependent scheduling and link adaptation. An SRS may also beused for the base station to obtain CSI estimation for DL under the caseof channel reciprocity.

With respect to CSI feedback in LTE, DL channel-dependent scheduling isa feature of LTE. In DL channel-dependent scheduling, the DLtransmission configuration and related parameters can be selected basedon the instantaneous DL channel condition, including the interferencesituation for example. To support DL channel-dependent scheduling, agiven UE provides the CSI to the evolved Node B (eNB). The eNB uses theinformation for its scheduling decisions. The CSI may consist of one ormore pieces of information, such as, a rank indication (RI), a precodermatrix indication (PMI), or a channel-quality indication (CQI). The RImay provide a recommendation on the transmission rank to use, or mayprovide a number of preferred layers that should be used for PDSCHtransmission to the UE. The PMI may indicate a preferred precoder to usefor PDSCH transmission. The CQI may represent the highestmodulation-and-coding scheme to achieve a block-error probability of10%, for example at most. Together, a combination of the RI, PMI, andCQI forms a CSI feedback report to the eNB. The information included inthe CSI report may depend on the UE's configured reporting mode. Forexample, in some cases, RI and PMI do not need to be reported unless theUE is in a spatial multiplexing multi-antenna transmission mode.

A CSI report may be configured to be periodic or aperiodic by radioresource control (RRC) signaling. In some cases, CSI reporting usingPUSCH is aperiodic. For example, aperiodic reporting may be triggered bydownlink control information (DCI) formats, and can be used to providemore detailed reporting via PUSCH. A given UE may be semi-staticallyconfigured by a higher layer to feedback CQI, PMI, and corresponding RI,on the same PUSCH using one of various CSI reporting modes. Examples ofvarious CSI reports modes are depicted in Table 1 below.

TABLE 1 Example CQI and PMI Feedback Types for PUSCH CSI Reporting ModesPMI Feedback Type No PMI Single PMI Multiple PMI PUSCH Wideband Mode 1-0Mode 1-1 Mode 1-2 CQI (wideband CQI) Feedback UE Selected Mode 2-0 Mode2-2 Type (subband CQI) Higher Layer- Mode 3-0 Mode 3-1 Mode 3-2configured (subband CQI)Referring to Table 1, for each of the transmission modes in Table 1,different reporting modes are defined and supported on PUSCH.

With respect to periodic CSI Reporting using PUCCH, a given UE may besemi-statically configured by higher layers to periodically feedbackdifferent CSI components (e.g., CQI, PMI, and/or RI) on the PUCCH using,for example, the reporting modes shown in Table 2.

TABLE 2 Example CQI and PMI FeedbackTypes for PUCCH CSI Reporting ModesPMI Feedback Type No PMI Single PMI PUCCH CQI Wideband Mode 1-0 Mode 1-1Feedback Type (wideband CQI) UE Selected Mode 2-0 Mode 2-1 (subband CQI)Referring to Table 2, for each of the transmission modes in Table 2,different periodic CSI reporting modes are defined and supported onPUCCH.

With respect to three-dimensional (3D) beam systems (which can also bereferred to as beamforming systems), a 3D beam system can explore bothhorizontal and elevation (vertical) angles. In addition, 3D beamformingcan achieve a better degree of freedom as compared to traditional 2Dbeamforming systems that only consider horizontal angles. The 3Dbeamforming system may use Active Antenna System (AAS) technology toadjust antenna weights of horizontal antenna ports, and also the antennaelements in the vertical direction. A 3D beam can be characterized by abeam emission direction and a beamwidth ΔB. The beam emission directioncan be described by the horizontal and elevation angles, where ψrepresents the horizontal angle and θ represents the elevation angle.The beamwidth ΔB indicates how wide a 3D beam can span. In practice, a3D beam is distinguished by its 3 dB beamwidth. Thus, to summarize, a 3Dbeam can be characterized by the parameters of horizontal angle,elevation angle, and beamwidth (ψ, θ, ΔB).

Referring to FIG. 1, an example 3D beam 102 is depicted. As shown, theemission direction of the beam 102 can be distinguished by thehorizontal angle 104 (between the beam's projection on the x and y planeand the x-axis) and the elevation angle 106 (between the beam andz-axis).

Turning now to Full-Dimension (FD) Multiple-Input and Multiple-Output(MIMO), FD-MIMO typically includes a base station with a two-dimensionalantenna array that supports multi-user joint elevation and azimuthbeamforming. This may result in higher cell capacity compared toconventional systems in 3GPP release 12. In some cases, using FD-MIMOtechniques, LTE systems can achieve 3-5× performance gain in cellcapacity and cell edge throughput.

LTE release 10 has introduced a CSI-RS that can be used for DL channelCSI estimation for the UEs. There are up to 8 antenna ports specified inrelease 10 and up to 16 antenna ports specified in release 13.

SUMMARY

It is recognized herein that as the number of transmit antennas incellular systems (e.g., NR or 5G systems) increase, the reference signal(RS) overhead may increase to unacceptable levels. Embodiments describedherein provide an enhanced and more efficient design for Channel StateInformation (CSI) feedback as compared to current approaches.

In an example embodiment, a user equipment (UE) selects a subset ofantenna ports periodically or aperiodically. In some cases, the antennaports do not correspond to physical antennas. For example, the antennaports may be logical entities that are distinguished by their referencesignal sequences. The ports are used for future DL transmission. The UEindicates the selected antenna ports to a Transmission and ReceptionPoint (TRP), which can be referred to generally as a new radio (NR)node. For example, the TRP can be indicated via a TRP identity (ID). TheTRP ID can be explicitly signaled via radio resource control (RRC)signaling or a media access control (MAC) control element (CE)configuration. Alternatively, the TRP ID can be implicitly signaled viaa reference signal. UE-centric antenna port selection is used herein torefer to cases in which the UE selects antenna ports. The CSI report mayinclude a channel-quality indication (CQI), a precoder matrix indication(PMI), and/or a rank indication (RI), spatial information (SI) (e.g., aquasi-co-location (QCL) indication between antenna ports/beams), and theCSI report might only generated based on the selected antenna ports.Ports may be selected based on various criteria, as described herein.The UE may send an antenna port index report to the NR node to indicateto the NR node which ports are preferred. In another embodiment, the NRnode selects a subset of antenna ports for each UE to use for future DLtransmissions. This is referred to as network-centric antenna portselection.

In an example embodiment, a new CSI reporting contains beam indexfeedback to support beamforming training. In some cases, a given UE mayreport only the beam index or the UE may report the beam index and CQI.After receiving the UE's report, an NR node may choose the best beam fordata transmission or other beams in consideration of another UE'sperformance. Thus, for example, an apparatus (e.g., a UE) may select oneor more beams from a plurality of beams provided by nodes in thenetwork. The apparatus may send, to the nodes, a beam index feedbackwith a CSI report that indicates the selected one or more beams.Thereafter, the apparatus may receive, until a beam is reselected forexample, the channel state information reference signal and downlink(DL) data via only the selected one or more beams.

In one embodiment, an apparatus comprises a processor, a memory, andcommunication circuitry. The apparatus is connected to a network, forinstance a 5G network, via its communication circuitry. The apparatusfurther comprises computer-executable instructions stored in the memoryof the apparatus which, when executed by the processor of the apparatus,cause the apparatus to perform operations. The apparatus, which may be aUE, can receive, from a node on the network, a channel state informationreference signal associated with a full channel estimation. Based on thefull channel estimation, the apparatus may select one or more antennaports from a plurality of antenna ports. The apparatus may send, to thenode, an antenna port index report that indicates the selected one ormore antenna ports. Thereafter, until an antenna port is reselected, theapparatus may receive the channel state information reference signal viaonly the selected one or more antenna ports. In some cases, the one ormore antenna ports are selected based on predetermined criteria.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to limitations that solve anyor all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with accompanying drawingswherein:

FIG. 1 depicts an example three-dimensional (3D) beam;

FIG. 2 is a call flow for channel state information (CSI) feedback withUE-centric antenna port selection in accordance with an exampleembodiment;

FIG. 3 is a call flow for CSI feedback with network-centric antenna portselection in accordance with an example embodiment;

FIG. 4A illustrates one embodiment of an example communications systemin which the methods and apparatuses described and claimed herein may beembodied;

FIG. 4B is a block diagram of an example apparatus or device configuredfor wireless communications in accordance with the embodimentsillustrated herein;

FIG. 4C is a system diagram of an example radio access network (RAN) andcore network in accordance with an example embodiment;

FIG. 4D is another system diagram of a RAN and core network according toanother embodiment;

FIG. 4E is another system diagram of a RAN and core network according toanother embodiment; and

FIG. 4F is a block diagram of an exemplary computing system 90 in whichone or more apparatuses of the communications networks illustrated inFIGS. 2-4E may be embodied.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As further background, the 3rd Generation Partnership Project (3GPP)develops technical standards for cellular telecommunications networktechnologies, including radio access, the core transport network, andservice capabilities—including work on codecs, security, and quality ofservice. Recent radio access technology (RAT) standards include WCDMA(commonly referred as 3G), LTE (commonly referred as 4G), andLTE-Advanced standards. 3GPP has begun working on the standardization ofnext generation cellular technology, called New Radio (NR), which isalso referred to as “5G”. 3GPP NR standards development is expected toinclude the definition of next generation radio access technology (newRAT), which is expected to include the provision of new flexible radioaccess below 6 GHz, and the provision of new ultra-mobile broadbandradio access above 6 GHz. The flexible radio access may consist of anew, non-backwards compatible radio access in a new spectrum below 6GHz, and it may include different operating modes that can bemultiplexed together in the same spectrum to address a broad set of 3GPPNR use cases with diverging requirements. The ultra-mobile broadband mayinclude cmWave and mmWave spectrum that will provide the opportunity forultra-mobile broadband access for, for example, indoor applications andhotspots. In particular, the ultra-mobile broadband may share a commondesign framework with the flexible radio access below 6 GHz, with cmWaveand mmWave specific design optimizations.

As an initial matter, 3D Multiple-Input and Multiple-Output (MIMO) canbe referred to as 5G MIMO herein, such that the terms 3D MIMO and 5GMIMO can be used interchangeably without limitation.

It is recognized herein that a straightforward approach for implementing3D MIMO would be to assign one Channel State Information (CSI) ReferenceSignal (RS) (CSI-RS) port per each transmit antenna element. It isfurther recognized herein that in this approach, however, the number oftransmit antennas at a base station will be limited by the availablenumber of CSI-RS ports, and by the available resource elements in thetime-frequency resource block, which might not be possible from thepractical system design perspectives with larger number of antennas atthe base station. Currently, there are two approaches for a CSI-RSdesign for Full Dimension (FD) MIMO (FD-MIMO) to support up to 16antenna ports: beamformed CSI-RS and non-precoded CSI-RS schemes, andboth of which are now described by way of background.

With respect to current approaches to beamformed CSI-RS, in order toacquire relatively accurate 3D MIMO channel estimation and CSI, CSI-RSsymbols transmitted on the transmit antenna elements in every column areprecoded with the elevation beam weighting vector. Hence, for eachelevation beam, only one CSI-RS port is assigned to the transmit antennaelements in one column. All the horizontal ports are used and differentCSI-RS ports are used by different columns. Each column is precoded witha weighting vector to form the desired elevation beam.

With respect to current approaches to non-precoded CSI-RS, which canalso be referred to as Kronecker-Product (KP) based CSI framework,KP-based CSI-RS is based on the assumption that the 3D channel betweenan eNB and a UE can be approximated by the KP between the azimuth andelevation domain channels. The CSI-RS ports are transmitted on elementsin the vertical and horizontal axes of the array. A UE can be configuredwith multiple CSI processes, for example, one associated with theazimuth CSI-RS resource and another associated with the elevation CSI-RSresource. These CSI processes are used for obtaining precoderinformation for the azimuth and the elevation dimensions separately fromthe UE. At the eNB, the azimuth and the elevation precoder informationis used to form a 2D precoder with a Kronecker structure. Thus, withrespect to the KP-based CSI-RS scheme, the total number of CSI-RS portsrequired is equal to N_(h)-N_(v)−1, as compared to N_(h)N_(v) when usingthe straightforward approach.

It is recognized herein that the number of transmit antennas at the basestation may be increased, for example, to 32 antenna ports or greater.Further, beamformed CSI-RS and non-precoded CSI-RS may improve theabove-summarized schemes to support more antenna ports. Further still,with respect to future cellular systems, it is possible that asignificantly increased number of antennas may be implemented at thebase station to further increase cell capacity, for example, by 10×performance gain. For example, an eNB may use antenna arrays with a fewhundred antennas simultaneously serving many UEs in the sametime-frequency resource. Without being bound by theory, in an examplemassive MIMO system, as the number of the transmit antennas increases toinfinity (very large), cross-correlation of two random channelrealizations decreases to zero, and there will be no multi-userinterference resulting from co-scheduling and multiple access. This maygreatly improve the system throughput, and it may be energy-efficient,secure, robust, and efficient (e.g., use spectrum efficiently), whichmakes massive 3D MIMO a potentially key enabler for future cellularsystems.

Turning now to downlink control information (DCI), the DCI is currentlyformed and transmitted in a Physical Downlink Control Channel (PDCCH).The DCI format tells the UE how to get its data that is transmitted onthe Physical Downlink Shared Channel (PDSCH) in the same subframe. Itcarries the details for the UE such as, for example, number of resourceblocks, resource allocation type, modulation scheme, redundancy version,coding rate, etc., which may help a given UE find and decode the PDSCHfrom the resource grid.

As described further below, embodiments described herein may help enableenhanced mobile broadband (eMBB), Ultra-reliable and low latencycommunications (URLLC), and massive Machine Type Communications (mMTC).Example deployment scenarios for eMBB include, indoor hotspots, denseurban areas, rural areas, urban macro areas, and high speed areas.

A high density scenario generally refers to a situation with a highvolume of data traffic per area (traffic density) or a high number ofconnections (connection density). An example of a typical case is in anindoor office scenario, where users frequently upload and download datafrom the company's server, and real-time video conferences are alsoexpected. Another example use case is a hotspot scenario with high userdensity, wherein in the density may depend on the time of day (e.g.,morning, evening, weekday vs. weekend, etc.) and/or the location (e.g.,pedestrians in shopping mall, downtown street, stadium, users in busesin dense city center). In such scenarios, users may be indoor or outdoorwith static or low to medium mobility. High volume and high capacitymulti-media traffic uploading and downloading towards the Internet mightbe expected.

A higher user mobility generally refers to a user case in which enhancedmobile broadband for fast moving devices, such as vehicles (e.g., up to200 km/h) or trains (e.g, up to 500 km/h) are required. The typical userapplications include high quality mobile internet access, for example,to watch a high definition (HD) video, play an online game, participatein video conferencing, or receive enhanced navigation through instantand real-time information. Such mobile broadband may be provided to thefast moving users in various ways. For example, if an on-board basestation (or a relay) is available, the cellular network may be able toprovide a high-rate link to the road vehicle/train/aircraft. If anon-board station is not available, the user equipment in a given fastmoving road vehicle or train may have a direct link to the cellularnetwork.

It will be understood that embodiments described herein may also be tothe use case of Ultra-Reliable and Low Latency Communications (URLLC),in which accurate CSI feedback may be needed for highly reliabletransmission and sufficient coverage.

In the current 3GPP system, a UE performs the DL channel qualityestimation using the CSI-RS transmitted from the base station. Based onthe channel estimation, the UE generates a CSI report that includes achannel-quality indication (CQI), a precoder matrix indication (PMI),and/or a rank indication (RI) depending on higher layer configurationand transmission modes.

Generally, to take advantage of more transmit antenna ports, a codebookwith a larger size may be used, whereby more bits may be required forPMI reporting, in some cases. For example, the size of PMI reporting maybe 8 to 11 bits for 16 transmit antenna ports depending on differentnumbers of layers. For example, for 4 transmit antenna ports, the sizeof PMI reporting may be 4 to 8 bits. In some cases, the antenna ports donot correspond to physical antennas. For example, the antenna portsreferenced herein may be logical entities that are distinguished bytheir reference signal sequences.

For example, in some cases, with respect to single layer transmission,the sizes of PMI reporting for 4 and 16 transmit antenna ports are 8 and11 bits, respectively. With respect to NR MIMO, for example due to themassive number of transmit antennas, the antenna ports may be more than16 ports (e.g., 32, 64, 128, 256 or 1024 ports). Thus, it is recognizedherein that the size of the codebook and the size of PMI reporting mightincrease dramatically. Moreover, because of the large overhead ofCSI-RS, it is recognized herein that the full downlink channelestimation may become unrealistic in some cases. In addition to the PMIfeedback overhead increasing for massive MIMO, the other feedback (e.g.,CQI, RI, etc.) may also contribute to an issue with the CSI feedbackoverhead.

In some cases that include high traffic density and high user mobility,to achieve a reliable, high throughput eMBB DL transmission, frequentCSI reporting might be necessary. In a high connection density scenario,the large amount of users may cause an increasing of CSI reporting inthe network. It is recognized herein that the increased overhead of CSIreporting may lead to a substantial loss in maximum data throughput, andmay lead to a failure to meet eMBB high data rates and high densityrequirements.

Embodiments described herein include CSI reporting that achievesdesirable DL performance while keeping the overhead of CSI sufficientlylow. CSI reports, in accordance with various embodiments, may include achannel-quality indication (CQI), a precoder matrix indication (PMI),and/or a rank indication (RI), spatial information (SI) (e.g., such as aquasi-co-location (QCL) indication between antenna ports/beams).

Referring now to FIG. 2, an example system 200 is shown that includes anNR node 202 and a plurality of mobile devices or UEs 204 whichcommunicate in a network. The terms NR node, eNB, and Transmission andReception Point (TRP) may be used interchangeably herein, withoutlimitation. To illustrate, FIG. 2 depicts the NR node 202 as an NR/TRP202. It will be appreciated that the example system is simplified tofacilitate description of the disclosed subject matter and is notintended to limit the scope of this disclosure. Other devices, systems,and configurations may be used to implement the embodiments disclosedherein in addition to, or instead of, a system such as the systemillustrated in FIG. 2, and all such embodiments are contemplated aswithin the scope of the present disclosure.

Still referring to FIG. 2, in accordance with the illustratedembodiment, CSI feedback overhead is reduced with UE-centric antennaport selection. In accordance with the illustrated embodiment, forexample to enable UE-centric antenna port selection, the NR node 202, at206, transmits a Channel State Information Reference Signal (CSI-RS)through at least one, for instance all, available ports for NR CSI-RS.Thus, each UE of the plurality 204 can obtain a full channel estimation.The NR node may transmit the NR CSI-RS at 206 for the full channelestimation with a long duration. Alternatively, or additionally, NRCSI-RS at 204 may be triggered aperiodically by the NR node 202, or by arequest from a given UE. The CSI-RS that is sent (at 206) to a given UEof the plurality 204 may be specific to the UE or may be non-UEspecific. The CSI-RS at 206 may be unprecoded or may be a beamformedCSI-RS. Thus, the UE 202 may receive, from a node on the network aCSI-RS associated with a full channel estimation.

Based on the full channel estimation, at 208, each of the UEs 204 mayselect the best antenna ports, from a plurality of antenna ports,according to various pre-defined criteria, which is described furtherbelow. In accordance with the illustrated example, at 210, each UEsignals (e.g., sends) the indices of the selected antenna ports to theNR node/TRP 202. These indices may be transmitted through an uplinkcontrol channel or via other messages. For example, an antenna portindex report may indicate the selected one or more antenna ports. Forexample, the uplink control channel can be a new or reused UCI formatcarried on PUCCH or PUSCH, or any uplink control channels in a 5G systemfor example. Example details related to signaling the indices from theUE is described below. Still referring to FIG. 2, it will be understoodthat the above-described messaging may be performed periodically with alonger duration than the CSI reporting duration, or aperiodicallytriggered by, for example, the NR node/TRP 202 or the UEs 204 (via arequest). In an example, the CSI-RS may be received by the UE 202 viaonly the selected one or more antenna ports until an antenna port isre-selected.

With continuing reference to FIG. 2, upon selecting the antenna ports, agiven UE may calculate (at 214) and report (at 216) the CQI and/or PMIand RI on the selected antenna ports until the next antenna portre-selection is triggered. In some cases, at 212, the NR node 202 maysend the CSI-RS only on the selected antenna ports, thereby reducingCSI-RS overhead until the next antenna port re-selection. An antennaport re-selection may be scheduled periodically, or may be triggered bythe NR node 202 or a given UE.

In one embodiment, a new field (referred to as“antennaPortSelectionMode”) is used in radio resource control (RRC)signaling. The new field may have a length of 2 bits, or may have anyalternative length as desired. In one example, the first bit of the newfield indicates whether antenna port selection (APS) is enabled. When itis enabled, the second bit may indicate whether UE-centric ornetwork-centric APS is performed. As described further below, innetwork-centric APS, the network may select the antenna ports for DLtransmission. In an example UE-centric APS, the UE selects the antennaports based on a full channel CSI-RS.

As described above, an initial antenna port selection or an antenna portreselection may be triggered by the NR node 202 or one of the UEs 204.In one embodiment, a new field (referred to as “aps-trigger”) isdefined. For example, this field may have a length of 1 bit (or more),and it may be signaled as a new field in DCI (or UCI) formats viadownlink (or uplink) control channels, RRC signaling, or a media accesscontrol (MAC) layer control element (CE). In some cases, upon receivingthe trigger, the NR node 202 transmits the CSI-RS through availableantenna ports, for instance all available antenna ports, and the UEs 204perform the above-described operations (with reference to FIG. 2) toreselect antenna ports.

Turning now to examples of Antenna Port Selection Criteria (APSC), toreduce the CSI feedback overhead, a given UE may select a subset of theavailable antenna ports, for instance at 208. The subset may be used inthe CSI feedback calculation at 214 and future downlink transmissions.Example criteria is described below, but it will be understood thatother criteria may be used as desired. The criteria may be categorizedinto fixed-number APSC and dynamic-number APSC, where the differencebetween the categories is whether the number of selected antenna portsis fixed or dynamic.

With respect to fixed-number APSC, the number of selected antenna portsmay be configured by higher layer signaling or transmitted to a given UEvia NR downlink control channels. For example, the number of selectedports: may be pre-defined in a new field “numberSelectedAntennaPorts” inRRC signaling; may be updated through a MAC CE; or may be added to otherDCI formats as new fields or included in a new special DCI format thatis sent from the NR node 202 to the UE via the NR DL control channel.

Referring to Table 3 below, an example “number of selected antennaports” field in a new or reused DCI format is shown. As described above,this information can be periodically or aperiodically transmitted, forexample, via PDCCH or ePDCCH or any future 5G (DL) control channels.

TABLE 3 Example of Number of Selected Antenna Ports Field in a DCIFormat Field Name Length (Bits) Number of Selected Antenna Ports 4 MCS 5PMI confirmation for precoding 1 . . . . . .

Given the number of selected antenna ports, in some cases, a given UEmay obtain the optimal subset of antenna ports by solving the followingoptimization problem:

$\begin{matrix}{{\underset{s}{maximize}\mspace{14mu}{f(S)}}{{{{{subject}\mspace{14mu}{to}\text{:}\mspace{11mu} S} \Subset {A\mspace{14mu}{and}\mspace{14mu}{S}}} = s},}} & (1)\end{matrix}$where A is the set of all available antenna ports, and s is the numberof selected antenna ports. The objective function ƒ(S) may be defined invarious ways, for example and without limitation:

-   -   The capacity of the channel between the antenna ports in S and        the receive antenna.    -   The received SNR (or CQI) of the channel between the antenna        ports in S and the receive antenna.    -   The negative of the bit error rate (BER) of the channel between        the antenna ports in S and the receive antenna.

With respect to dynamic-number APSC, the number of selected antennaports is not fixed, and may depend on channel conditions andconfigurations. In one example, the NR node/TRP 202 may signal both oreither one of the maximum and minimum numbers of selected antenna ports(s_(max) and s_(min)) that a given UE must support, and the UE selects anumber N antenna ports such that s_(min)≤N≤s_(max). Thus, UE-selectedone or more antenna ports may total a number at least equal to theminimum number and no greater than the maximum number. The upperboundand lowerbound of antenna ports may be predefined in RRC signaling orvia a MAC CE, for example, or transmitted to the UE as new fields in aDCI format or a new DCI format via NR DL control channels. An example ofmaximum and minimum numbers of selected antenna ports fields in a new orreused DCI format is illustrated in Table 4.

TABLE 4 Example of Max and Min Numbers of Selected Antenna Ports Fieldsin a DCI Format Field Name Length (Bits) Maximum number of selectedantenna ports 4 Minimum number of selected antenna ports 4 MCS 5 PMIconfirmation for precoding 1 . . . . . .

Referring to Table 4, the optimization problem from (1) may become:

$\begin{matrix}{{\underset{s}{maximize}\;\frac{f(S)}{S}}{{{{subject}\mspace{14mu}{to}\text{:}\mspace{14mu} S} \Subset {{A\mspace{11mu}{and}\mspace{14mu} s_{m\; i\; n}} \leq {S} \leq s_{{ma}\; x}}},}} & (2)\end{matrix}$where s_(min) and s_(max) are the minimum and maximum numbers ofselected antenna ports, respectively.

As another example of dynamic-number APSC, a given UE may select antennaports that exceed one or more thresholds (e.g., an SNR threshold) toenhance the NR node/TRP's scheduling flexibility. Similarly, thethreshold may be predefined in RRC signaling or sent to the UE as newfields in a DCI format or a new DCI format via PDCCH, ePDCCH, or anyfuture 5G downlink control channel. In some cases, the threshold may beapplied together with other APSC to discard weak antenna ports, forexample, by selecting s antenna ports from those having a SNR greaterthan the threshold:

$\begin{matrix}{{\underset{s}{maximize}\mspace{14mu}{f(S)}}{{{{{subject}\mspace{14mu}{to}\text{:}\mspace{11mu} S} \Subset {A^{\prime}\mspace{14mu}{and}\mspace{14mu}{S}}} = s},}} & (3)\end{matrix}$where A′ is the set of antenna ports whose SNR is greater than thethreshold.

With respect to a frequency non-selective channel, the objectivefunction f(S) may be the same for all subbands, and the antenna portselection may be optimized for the wideband. With respect to a frequencyselective channel, when subband antenna port selection is required, insome cases, the antenna port selection may be optimized for eachsubband, and sent to the NR node/TRP individually. In some cases inwhich wideband antenna port selection is required for a frequencyselective channel, the objective function may be the summation of theobjective functions on each subband, for example:ƒ(S)=Σ_(i=1) ^(K)ƒ_(i)(S)  (4)where K is the number of subbands and f_(i) is the objective function atthe i-th subband.

With respect to two-level beamforming training, the wider beam training(or beam sweeping) and the narrower beam training (or beamformingtraining) may be configured individually as above. In some cases, eachbeamforming level may be configured to either fix-number APSC ordynamic-number APSC. For example, the numbers of selected antenna portss_(wider) and s_(narrower) for the wider and narrower beam training,respectively, may be signaled to the UE. Then the UE may selects_(wider) and s_(narrower) antenna ports in the wider and narrower beamtraining, respectively.

Turning now to the antenna port index report that is sent at 210 in FIG.2, for example, upon selecting antenna ports (at 208), for instanceaccording to the criteria described above, the UE may need to feedbackthe antenna port selection to the NR node/TRP 202. In some cases, thisantenna port selection is used in downlink RS and data transmissionsuntil the next antenna port selection is available. Example mechanismsto feedback the antenna port selection to the NR node/TRP 202 are nowdiscussed.

In one example, the selected antenna port indices are represented by abit-map. For example, an N-bit binary sequence may be used to feedbackthe selected antenna port indices for N available antenna ports, whereeach bit represents one antenna port and “1” indicates that thecorresponding antenna port is selected. Furthermore, for fixed-numberAPSC, to select s antenna ports out of N available antenna ports, thereare a total of

$\quad\begin{pmatrix}N \\s\end{pmatrix}$possible selections. The selection may represented by a

${\left\lceil {\log_{2}\begin{pmatrix}N \\s\end{pmatrix}} \right\rceil - {{bit}\mspace{14mu}{binary}\mspace{14mu}{sequence}}},$which is less than N bits for the bit-map representation. By way ofexample, to select four out of a total of 16 available antenna ports, itmay require

$\left\lceil {\log_{2}\begin{pmatrix}16 \\4\end{pmatrix}} \right\rceil = 11$bits to feedback antenna port selection; less than 16 bits for thebit-map representation.

In another example embodiment of an antenna port index report, the totalnumber of possible antenna port selections is decreased, for example, toreduce the overhead of the antenna port index report and to reduce thecomplexity of finding the best available antenna port selection. In somecases, the optimization problem (1) can be expressed as

$\underset{s}{maximize}\;{f(S)}$ subject  to:  S ∈ ℱ,where

is a family of sets over A, e.g., a set of subsets of A. According todifferent

, there may be different forms of antenna port index reports to reducethe overhead. For example, the available antenna ports may bepartitioned into groups A₁, A₂, . . . , A_(s), such that only oneantenna port can be selected from each group, e.g.,

={(a _(1,j) ₁ ,a _(2,j) ₂ , . . . ,a _(s,j) _(s) ),∀a _(i,j) _(i) ∈A_(i)}Thus, in an example,

$s\left\lceil {\log_{2}\frac{N}{s}} \right\rceil$bits may represent every possible selection for N available antennaports. For example, to select 4 out of 16 antenna ports, an 8-bit binarysequence may be sufficient to represent the selection, which is lessthan the 16-bit binary sequence for a bit-map.

As yet another example, antenna port selections may be predefined, and agiven UE may be required to choose a selection from them and onlyfeedback the index associated with the selection. In this case,

is the set of all predefined antenna port selections. The required sizeof the feedback may depend on

, which is less than the size of the bit-map representation. It will beunderstood that the above-described mechanisms may reduce the overheadof the antenna port index report. They may also, in some cases, limitthe UE's flexibility to make antenna port selections.

As described above, antenna port selection (APS) reporting may beperiodic or aperiodic. A higher layer may configure APS for a given UE.With respect to spatial multiplexing transmission modes, the APS may bereported when the UE is configured with PMI/RI reporting. For aperiodicCQI/PMI reporting, in some cases, APS reporting is transmitted only ifthe configured CSI feedback type supports APS reporting.

The channel coding for APS reporting may be chosen for high reliability(e.g., like RI reporting). For example, if the APS feedback consists of1-bit or 2-bits of information, it may be encoded by a repetition codewith some scrambling bits. If APS reporting consists of more informationbits, it may be encoded by a linear error-correcting code (e.g.,Reed-Muller code), or it may be partitioned into smaller information bitsequences. Each smaller sequence may be encoded by a linearerror-correcting code (e.g., Reed-Muller code). The final outputsequence may be obtained by interleaving the concatenation and circularrepetition of the linear encoded sequences.

With respect to aperiodic CQI/PMI reporting (e.g., at 216), in somecases, APS feedback is transmitted only if the configured CSI feedbacktype supports APS reporting. The APS feedback may be transmitted withother CSI reporting, such as CQI, PMI, over NR uplink data channel.Example APS feedback types are described below, without limitation:

-   -   APS feedback type 0 (No APS): No APS reporting.    -   APS feedback type 1 (Single APS): A set of antenna ports is        selected from the available antenna ports assuming transmission        on the whole band.    -   APS feedback type 2 (Multiple APS): For each subband, a set of        antenna ports is selected from the available antenna ports        assuming transmission only in the subband.

In an example, the APS feedback type may be combined with the CQIfeedback type and PMI feedback type to form an NR CSI reporting mode(e.g., Mode i-j-k, where i=1, 2, or 3 and indicates the CQI reportingtype, j=0, 1, or 2 and indicates the PMI reporting type, and k=0, 1, or2 and indicates the APS reporting time. In an example, i is set to: 1 toindicate a wideband report, 2 to indicate a UE-selected report, and 3 toindicate a higher-layer configured report. In an example, j is set to: 0to indicate no PMI report, 1 to indicate a single PMI report, and 2 toindicate multiple PMI reports. In an example, k is set to: 0 to indicateno APS report, 1 to indicate a single APS report, and 2 to indicatemultiple APS reports. The CQI and PMI may be calculated based on theselected antenna ports. In some cases, the NR CSI reporting mode may beconfigured by higher layer signaling.

With respect to periodic CSI Reporting with APS feedback, a given UE maybe configured by higher layer to periodically feedback different CSIcomponents including, for example, the APS report via PUCCH or other 5Gcontrol channels. Example APS feedback types are described below,presented without limitation:

-   -   APS feedback type 0 (No APS): No APS reporting, and UE reports        CQI, PMI and/or RI based on all antenna ports.    -   APS feedback type 1 (Single APS): A set of antenna ports is        selected from the available antenna ports assuming transmission        on the whole band.        In some cases, the APS feedback type may be combined with the        CQI feedback type and PMI feedback type to form an NR CSI        reporting mode. (e.g., Mode i-j-k, where i=1, 2 indicates the        CQI reporting type (e.g., 1 for wideband report and 2 for        UE-selected report); j=0,1 indicates the PMI reporting type        (e.g., 0 for no PMI report and 1 for single PMI report); and        k=0,1 indicates the APS reporting type (e.g., 0 for no APS        report and 1 for single APS report). CQI and PMI may be        calculated based on the selected antenna ports. It will be        understood that the NR CSI reporting modes may vary as desired.        The NR CSI reporting mode is configured by higher layer        signaling.

Example New NR uplink control channel reporting types for APS feedbackare listed in Table 5 below, without limitation.

TABLE 5 Example PUCCH Reporting Types Related to APS Feedback PUCCHReporting Type Reported Item 11 APS 14A APS/RI 14B APS/PMI 14C APS/CQI .. . . . .

For a UE configured with APS reporting, the periodicity M_(APS) andrelative offset N_(OFFSET,APS) (in a given time unit for examplesubframes or time interval X or OFDM symbols) for APS reporting may beconfigured by higher layer signaling. For example, the informationconcerning the periodicity and relative offset of APS reporting may beprovided by RRC signaling through a field aps-ConfigIndex, which can bea part of the CQI-ReportPeriodic in CQI-ReportConfig, as shown in Table6. For example, examples of reporting instances for CQI, PMI, RI and APSare shown below:

In an example case where wideband CQI/PMI reporting is configured, thereporting interval of wideband CQI/PMI reporting is a period N_(pd) (inthe given time unit). The reporting instances for wideband CQI/PMI maybe time units satisfying the following equation, where n_(t) is the timeunit index:(n _(t) −N _(OFFSET,CQI))mod(N _(pd))=0.In an example case in which RI reporting is configured, the reportinginterval of RI reporting is an integer multiple M_(RI) of period N_(pd)(in the given time unit). The reporting instances for RI may be timeunits satisfying the following equation, for example:(n _(t) −N _(OFFSET,CQI) −N _(OFFSET,RI))mod(N _(pd) ·M _(RI))=0.In an example case in which APS reporting is configured, the reportinginterval of APS reporting is an integer multiple M_(APS) of periodN_(pd)·M_(RI) (in the given time unit). The reporting instances for APSmay be time units satisfying the following equation, for example:(n _(t) −N _(OFFSET,CQI) −N _(OFFSET,RI) −N _(OFFSET,APS))mod(N _(pd) ·M_(RI) ·M _(APS)=)0.

TABLE 6 Exemplary CQI-ReportConfig Information Element with Proposed APSFeedback -- ASN1START CQI-ReportConfig ::= SEQUENCE {cqi-ReportModeAperiodic CQI-ReportModeAperiodic OPTIONAL, -- Need ORnomPDSCH-RS-EPRE-Offset INTEGER (−1. .6), cqi-ReportPeriodicCQI-ReportPeriodic OPTIONAL -- Need ON } . . . CQI-ReportPeriodic ::=CHOICE { release NULL, setup SEQUENCE { cqi-PUCCH-ResourceIndex INTEGER(0. .1185). cqi-pmi-ConfigIndex INTEGER (0. .1023).cqi-FormatIndicatorPeriodic CHOICE { widebandCQI NULL, subbandCQISEQUENCE { k INTEGER (1. .4) } }, ri-ConfigIndex INTEGER (0. .1023)OPTIONAL, --Need OR aps-ConfigIndex INTEGER (0. .1023) OPTIONAL,simultaneousAckNackAndCQI BOOLEAN } } CQI-ReportModeAperiodic ::=ENUMERATED { rm12, rm20, rm22, rm30, rm31, rm32-v1250, rm10-v1310,rm11-v1310 } . . . -- ASN1STOP

An example that demonstrates the efficiency of the CSI feedbackmechanisms is now described to further illustrate the described-hereinembodiments, without limitation. By way of example, suppose the NRnode/TRP 202 is equipped with 16 antenna ports, and legacy orthogonalCSI-RS is applied. The overheads of the legacy CSI report for the fullchannel and the proposed CSI report for the channel of the best 4antenna ports can be compared. Assume that the periodicities of CQI/PMIand RI are 10 and 80 ms (subframes), and the selected antenna portindices are reported with the periodicity of 320 ms (subframes).Compared to the legacy CSI report, the overhead of CQI and RI reportingis the same, for example, because their periodicities and sizes are notchanged. Thus, in this example, only the overhead reduction for PMI andantenna port selection reports is considered. In PMI calculation, thecodebooks defined in Release 14 may be used, and the size of the PMI maybe 8 bits and 11 bits for 4 and 16 antenna ports, respectively.

Continuing with the example, if a periodic CSI report is configured fora UE-selected CSI report, the total bandwidth may be divided intomultiple, for instance 4, bandwidth parts. In an example, the UE reportsCQI and PMI for each bandwidth part to cycle through the four bandwidthparts. For the legacy CSI report, the total bits for PMI reports for 16antenna ports in every 320 subframes is 11×4×32=1408 bits. For oneembodiment described above, when the UE reports the antenna portselection for the wideband, the total bits in every 320 subframes is8×433 32+11=1035, where the 11 bits are for the antenna port indexreport as described above. Thus, in the example, the total bits for PMIreports is 26.5% less than that for the legacy PMI report, and it isrecognized herein that the savings can be greater, for instance asapplied to a larger antenna array.

If a periodic CSI report is configured for a wideband CSI report, thesingle CQI and single PMI may be reported for the whole band. For legacyCSI report, in some cases, the total bits for PMI reports for 16 antennaports in every 320 subframes is 11×32=352 bits. In contrast, in anexample embodiment, the total bits in every 320 subframes is8×32+11=267, where the 11 bits are for the antenna port index report asdescribed above. Thus, in an example, the total bits for PMI reports are24.1% less than that for the legacy PMI report, and it is recognizedherein that the savings can be greater, for instance as applied to alarger antenna array.

Thus, as shown, the bit size for PMI reporting may be reduced and theefficiency may depend on the details of configuration, antenna portselection, and reporting mechanisms. It will be appreciated that theabove-described embodiments can also be applied to other CSI-RS schemes,such as KP-based CSI-RS and beamformed CSI-RS schemes.

Referring now to FIG. 3, an example of CSI Feedback with network-centricAntenna Port Selection is shown in the example system 200. In accordancewith the illustrated embodiment, a new CSI feedback mechanism reducesCSI feedback overhead with network-centric antenna port selection. Asshown, the NR node 202 may obtain the full uplink channel estimation, at302, from the uplink sounding reference signals (SRS) transmitted byeach of the UEs 204. It may be performed periodically with a longduration or aperiodically. In some cases, for a time division duplex(TDD) system, the NR node 202 takes advantage of the full channelreciprocity feature by using the uplink channel CSI obtained from theuplink SRS (received at 302) as the downlink channel CSI. Then, the NRnode 202 can perform antenna port selection at 304 using the receivedCSI. In some cases, for a frequency division duplex (FDD) system, the NRnode 202 transmits (e.g., at 306) the NR CSI-RS on all antenna ports,and the UEs 204 may feedback the CSI report (e.g., at 310) based on theprocessing of the received CSI-RS.

Still referring to FIG. 3, based on the full channel estimation receivedat 310, the NR node 202 selects (at 312) the best antenna portsaccording to, for example, the pre-defined criteria. The APSC for NRnode/TRP-centric antenna port selection may be the same as that forUE-centric antenna port selection described above with reference to FIG.2. Alternatively, or additionally, the NR node 202 may also considerother criteria, e.g., assigning two UEs to different beams to mitigateinterference between them. In some cases, for example at 314, the NRnode 202 only transmits the NR CSI-RS and downlink data on the antennaports selected at 312 and/or 304. In accordance with the example, the UEcalculates (e.g., at 316) and reports CQI and/or PMI and RI (e.g., at318) only based on the current antenna port selection until the nextantenna port re-selection is performed. The antenna port re-selectionmay be scheduled periodically, or triggered by the NR node 202 or one ormore of the UEs 204. The NR node 202 can configure CSI-RS resources viaRRC signaling, for example, and dynamically activate selected CSI-RSresources to the UE 204 via a DCI indication. Thus, the UE 204 maymeasure those CSI-RS resources dynamically allocated/configured by NRnode 202. In addition, in some cases, the UE 204 can jointly feedback tothe NR node 202, with CQI and/or PMI, RI, CSI-RS identification based onbest-M CSI-RS. The M value can be specified via configuration initiallyby RRC signalings or via MAC CE. Because the value M value can beconfigured by the NR node 202, the NR node 202 may know the joint CSIfeedback information. In some cases, the joint CSI feedback informationcan be jointly encoded by using polar coding. For example, the NR node202 can activate N=8 CSI-RS for the UE 204 performing CSI measurement,and can report the best M=2 for CSI reporting. In an example, the UE 204uses a bit mapping (b_(N-1) b_(N-2) . . . b₀) to indicate whichconfigured CSI-RS resources are fed back. For example, the CSI feedbackinformation can be constructed as (b_(N-1) b_(N-2) . . . b₀)+(d_(1,Q-1)d_(1,Q-2) . . . d_(1,0))+ . . . +(d_(M,Q-1) d_(M,Q-2) d_(M,0)), whered_(i,j) denotes the j-th feedback bits of i-th CSI-RS, 1≤i≤N.

An initial antenna port selection or an antenna port reselection may betriggered by the NR node/TRP 202 or the UEs 204. A new field (e.g,“aps-trigger”) may be defined with the length of 1 bit (or more). In anexample, it may be signaled as a new field in DCI (or UCI) formats viadownlink (uplink) control channel or RRC signaling or va a MAC CE. Uponreceiving the trigger, the NR node/TRP may perform the above-describedsteps to reselect antenna ports.

It will be understood that the embodiment described with reference toFIG. 3 can further reduce the overhead of CSI feedback, for example,because the antenna port index report might not be necessary, in somecases. Therefore, even with a large number of transmit antenna ports,the CSI report overhead can be reduced significantly.

Turning now to CSI Feedback to Support Beam Sweeping and BeamformingTraining, in 5G, beamforming training is a procedure to discover thebest beam direction between the transmitter and receiver pair.Beamforming training begins with the NR node transmitting the RS throughall available beams or a subset of available beams, and a given UE feedsback the index of the best beam. Then, in typical beamforming training,the NR node continues to send out the RS through narrower beams orneighboring beams according to UE's feedback to enable further aligningor tuning of the beam directions. Enhanced CSI feedback to support beamsweeping and beamforming training is now described, in accordance withan example embodiment. By way of example, referring to the examplesystem 200, the NR node 202 can configure certain CSI-RS resources(e.g., (via RRC signaling or MAC-CE), and can use DCI to dynamicallyactivate those configured CSI-RS resources for the UE 204. Theconfigured CSI-RS resources can be from a TRP or multiple TRPs. In somecases, the configured CSI-RS resources can be dynamically activated viaa primary TRP and/or secondary TRPs. In an example, if the UE 204 has toreport more than 2 CSI feedbacks, and those CSI feedbacks are comingfrom different TRPs, then the beam ID and the TRP identity (ID) may beassociated with the CSI report, which may also include CQI and/or PMI,RI. In some cases, the TRP ID can be indicated via the configuration ofthe CSI reference signal.

In an example, the feedback report is configured by higher layers andcontains the beam index (BI) and the corresponding CQI on the uplinkcontrol channel or data channel. Example CSI reporting modes are givenin Table 7 below, presented without limitation:

TABLE 7 Example CQI and BI Feedback Types for Example CSI ReportingModes to Support Beam Sweeping and Beamforming Training Beam IndexFeedback Type No BI Single BI CQI Wideband Mode 4-0 Mode 4-1 FeedbackType (wideband CQI) UE Selected Mode 5-0 Mode 5-1 (subband CQI)Referring to Table 7, the UE may report M BIs and/or CQIs, where M isconfigurable. In some cases, the CQI might not need to be reported.Thus, in some cases, the UE may report the BI only or the BI and theCQI. In an example, the channel coding for the BI may be chosen for highreliability. Further, when a given UE detects beams from differenttransmission/reception points (TRP), it may feedback the TRP index inaddition to the BI to enable multiple points of transmission orreception. Still referring to Table 7, with respect to Mode 4-1, thewideband CQI may be calculated assuming the transmission is on the wholeband with the reported beam. For Mode 5-1, the subband CQI may becalculated, for example, assuming the transmission is only on thecorresponding subband with the reported beam. For a different subband,the UE may report difference beam indices. After receiving the UE'sreport, the NR node may choose the best beam for data transmission, orthe UE may choose a beam based on other performance factors associatedwith the UE. During data transmission, the UE or NR node may requestbeam re-selection for various reasons such as, for example and withoutlimitation, performance degradation or location change. The beamre-selection may start with a new beam sweep or beamforming training. Insome cases, when the UE decides to request a beam re-selection, it mayfeedback a two-bit information “beamReselectionRequest” through the NRuplink control channel, where the first bit indicates the request, andthe second bit indicates whether the reselection starts from a beamsweep stage. The channel coding of the beam re-selection request may bechosen for high reliability. The beam re-selection may also beconfigured by higher layer signaling such as RRC signaling or via a MACCE. By way of example, a new field “beamReselectionPeriod” is definedherein to indicate the periodicity of an example beam re-selection. The“beamReselectionRequest” feedback can be jointly fedback, for example,when UE 204 monitors multiple TRPs and each TRP configures differentCSI-RS resources for the UE 204, while performing beam management.

Thus, in an example embodiment, an apparatus (e.g., a UE) may select oneor more beams from a plurality of beams provided by at least one node inthe network. The apparatus may send, to the at least one node, a beamindex feedback with a channel state information (CSI) report thatindicates the selected one or more beams. The apparatus may receive,until a beam is reselected, a channel state information reference signaland downlink (DL) data via only the selected one or more beams. Further,in some cases, the apparatus may detect a plurality of beams from aplurality of nodes. Thus, the apparatus may send, to the plurality ofnodes, an index (e.g., TRP ID) associated with each node that isassociated with at least one of the one or more selected beams. In anexample, the CSI report includes a respective index associated with apreconfigured number of beams. The apparatus may also send a beamre-selection request, via an uplink control channel, to the at least onenode. As described above, the beam re-selection request may include afirst bit that indicates that the beam should be re-selected, and asecond bit that indicates whether the beam should be re-selected using anew beam sweep. The beam may be re-selected in accordance with apreconfigured periodicity.

The 3rd Generation Partnership Project (3GPP) develops technicalstandards for cellular telecommunications network technologies,including radio access, the core transport network, and servicecapabilities—including work on codecs, security, and quality of service.Recent radio access technology (RAT) standards include WCDMA (commonlyreferred as 3G), LTE (commonly referred as 4G), and LTE-Advancedstandards. 3GPP has begun working on the standardization of nextgeneration cellular technology, called New Radio (NR), which is alsoreferred to as “5G”. 3GPP NR standards development is expected toinclude the definition of next generation radio access technology (newRAT), which is expected to include the provision of new flexible radioaccess below 6 GHz, and the provision of new ultra-mobile broadbandradio access above 6 GHz. The flexible radio access is expected toconsist of a new, non-backwards compatible radio access in new spectrumbelow 6 GHz, and it is expected to include different operating modesthat can be multiplexed together in the same spectrum to address a broadset of 3GPP NR use cases with diverging requirements. The ultra-mobilebroadband is expected to include cmWave and mmWave spectrum that willprovide the opportunity for ultra-mobile broadband access for, e.g.,indoor applications and hotspots. In particular, the ultra-mobilebroadband is expected to share a common design framework with theflexible radio access below 6 GHz, with cmWave and mmWave specificdesign optimizations.

3GPP has identified a variety of use cases that NR is expected tosupport, resulting in a wide variety of user experience requirements fordata rate, latency, and mobility. The use cases include the followinggeneral categories: enhanced mobile broadband (e.g., broadband access indense areas, indoor ultra-high broadband access, broadband access in acrowd, 50+ Mbps everywhere, ultra-low cost broadband access, mobilebroadband in vehicles), critical communications, massive machine typecommunications, network operation (e.g., network slicing, routing,migration and interworking, energy savings), and enhancedvehicle-to-everything (eV2X) communications. Specific service andapplications in these categories include, e.g., monitoring and sensornetworks, device remote controlling, bi-directional remote controlling,personal cloud computing, video streaming, wireless cloud-based office,first responder connectivity, automotive recall, disaster alerts,real-time gaming, multi-person video calls, autonomous driving,augmented reality, tactile internet, and virtual reality to name a few.All of these use cases and others are contemplated herein.

FIG. 4A illustrates one embodiment of an example communications system100 in which the methods and apparatuses described and claimed hereinmay be embodied. As shown, the example communications system 100 mayinclude wireless transmit/receive units (WTRUs) 102 a, 102 b, 102 c,and/or 102 d (which generally or collectively may be referred to as WTRU102), a radio access network (RAN) 103/104/105/103 b/104 b/105 b, a corenetwork 106/107/109, a public switched telephone network (PSTN) 108, theInternet 110, and other networks 112, though it will be appreciated thatthe disclosed embodiments contemplate any number of WTRUs, basestations, networks, and/or network elements. Each of the WTRUs 102 a,102 b, 102 c, 102 d, 102 e may be any type of apparatus or deviceconfigured to operate and/or communicate in a wireless environment.Although each WTRU 102 a, 102 b, 102 c, 102 d, 102 e is depicted inFIGS. 4A-4E as a hand-held wireless communications apparatus, it isunderstood that with the wide variety of use cases contemplated for 5Gwireless communications, each WTRU may comprise or be embodied in anytype of apparatus or device configured to transmit and/or receivewireless signals, including, by way of example only, user equipment(UE), a mobile station, a fixed or mobile subscriber unit, a pager, acellular telephone, a personal digital assistant (PDA), a smartphone, alaptop, a tablet, a netbook, a notebook computer, a personal computer, awireless sensor, consumer electronics, a wearable device such as a smartwatch or smart clothing, a medical or eHealth device, a robot,industrial equipment, a drone, a vehicle such as a car, truck, train, orairplane, and the like.

The communications system 100 may also include a base station 114 a anda base station 114 b. Base stations 114 a may be any type of deviceconfigured to wirelessly interface with at least one of the WTRUs 102 a,102 b, 102 c to facilitate access to one or more communication networks,such as the core network 106/107/109, the Internet 110, and/or the othernetworks 112. Base stations 114 b may be any type of device configuredto wiredly and/or wirelessly interface with at least one of the RRHs(Remote Radio Heads) 118 a, 118 b and/or TRPs (Transmission andReception Points) 119 a, 119 b to facilitate access to one or morecommunication networks, such as the core network 106/107/109, theInternet 110, and/or the other networks 112. RRHs 118 a, 118 b may beany type of device configured to wirelessly interface with at least oneof the WTRU 102 c, to facilitate access to one or more communicationnetworks, such as the core network 106/107/109, the Internet 110, and/orthe other networks 112. TRPs 119 a, 119 b may be any type of deviceconfigured to wirelessly interface with at least one of the WTRU 102 d,to facilitate access to one or more communication networks, such as thecore network 106/107/109, the Internet 110, and/or the other networks112. By way of example, the base stations 114 a, 114 b may be a basetransceiver station (BTS), a Node-B, an eNode B, a Home Node B, a HomeeNode B, a site controller, an access point (AP), a wireless router, andthe like. While the base stations 114 a, 114 b are each depicted as asingle element, it will be appreciated that the base stations 114 a, 114b may include any number of interconnected base stations and/or networkelements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 b may be part of the RAN103 b/104 b/105 b, which may also include other base stations and/ornetwork elements (not shown), such as a base station controller (BSC), aradio network controller (RNC), relay nodes, etc. The base station 114 amay be configured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The base station 114 b may be configured to transmit and/orreceive wired and/or wireless signals within a particular geographicregion, which may be referred to as a cell (not shown). The cell mayfurther be divided into cell sectors. For example, the cell associatedwith the base station 114 a may be divided into three sectors. Thus, inan embodiment, the base station 114 a may include three transceivers,e.g., one for each sector of the cell. In an embodiment, the basestation 114 a may employ multiple-input multiple output (MIMO)technology and, therefore, may utilize multiple transceivers for eachsector of the cell.

The base stations 114 a may communicate with one or more of the WTRUs102 a, 102 b, 102 c over an air interface 115/116/117, which may be anysuitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, cmWave,mmWave, etc.). The air interface 115/116/117 may be established usingany suitable radio access technology (RAT).

The base stations 114 b may communicate with one or more of the RRHs 118a, 118 b and/or TRPs 119 a, 119 b over a wired or air interface 115b/116 b/117 b, which may be any suitable wired (e.g., cable, opticalfiber, etc.) or wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, cmWave,mmWave, etc.). The air interface 115 b/116 b/117 b may be establishedusing any suitable radio access technology (RAT).

The RRHs 118 a, 118 b and/or TRPs 119 a, 119 b may communicate with oneor more of the WTRUs 102 c, 102 d over an air interface 115 c/116 c/117c, which may be any suitable wireless communication link (e.g., radiofrequency (RF), microwave, infrared (IR), ultraviolet (UV), visiblelight, cmWave, mmWave, etc.). The air interface 115 c/116 c/117 c may beestablished using any suitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, 102 c, or RRHs 118 a, 118 b and TRPs 119 a, 119 b in the RAN103 b/104 b/105 b and the WTRUs 102 c, 102 d, may implement a radiotechnology such as Universal Mobile Telecommunications System (UMTS)Terrestrial Radio Access (UTRA), which may establish the air interface115/116/117 or 115 c/116 c/117 c respectively using wideband CDMA(WCDMA). WCDMA may include communication protocols such as High-SpeedPacket Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may includeHigh-Speed Downlink Packet Access (HSDPA) and/or High-Speed UplinkPacket Access (HSUPA).

In an embodiment, the base station 114 a in the RAN 103/104/105 and theWTRUs 102 a, 102 b, 102 c, or RRHs 118 a, 118 b and TRPs 119 a, 119 b inthe RAN 103 b/104 b/105 b and the WTRUs 102 c, 102 d, may implement aradio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA),which may establish the air interface 115/116/117 using Long TermEvolution (LTE) and/or LTE-Advanced (LTE-A). In the future, the airinterface 115/116/117 may implement 3GPP NR technology.

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement radio technologies such as IEEE 802.16 (e.g., WorldwideInteroperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×,CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95(IS-95), Interim Standard 856 (IS-856), Global System for Mobilecommunications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSMEDGE (GERAN), and the like.

The base station 114 c in FIG. 4A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In anembodiment, the base station 114 c and the WTRUs 102 e may implement aradio technology such as IEEE 802.11 to establish a wireless local areanetwork (WLAN). In an embodiment, the base station 114 c and the WTRUs102 e may implement a radio technology such as IEEE 802.15 to establisha wireless personal area network (WPAN). In yet an embodiment, the basestation 114 b and the WTRUs 102 c, 102 d may utilize a cellular-basedRAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish apicocell or femtocell. As shown in FIG. 4A, the base station 114 b mayhave a direct connection to the Internet 110. Thus, the base station 114c may not be required to access the Internet 110 via the core network106/107/109.

The RAN 103/104/105 and/or RAN 103 b/104 b/105 b may be in communicationwith the core network 106/107/109, which may be any type of networkconfigured to provide voice, data, applications, and/or voice overinternet protocol (VoIP) services to one or more of the WTRUs 102 a, 102b, 102 c, 102 d. For example, the core network 106/107/109 may providecall control, billing services, mobile location-based services, pre-paidcalling, Internet connectivity, video distribution, etc., and/or performhigh-level security functions, such as user authentication.

Although not shown in FIG. 4A, it will be appreciated that the RAN103/104/105 and/or RAN 103 b/104 b/105 b and/or the core network106/107/109 may be in direct or indirect communication with other RANsthat employ the same RAT as the RAN 103/104/105 and/or RAN 103 b/104b/105 b or a different RAT. For example, in addition to being connectedto the RAN 103/104/105 and/or RAN 103 b/104 b/105 b, which may beutilizing an E-UTRA radio technology, the core network 106/107/109 mayalso be in communication with another RAN (not shown) employing a GSMradio technology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d, 102 e to access the PSTN 108, the Internet110, and/or other networks 112. The PSTN 108 may includecircuit-switched telephone networks that provide plain old telephoneservice (POTS). The Internet 110 may include a global system ofinterconnected computer networks and devices that use commoncommunication protocols, such as the transmission control protocol(TCP), user datagram protocol (UDP) and the internet protocol (IP) inthe TCP/IP internet protocol suite. The networks 112 may include wiredor wireless communications networks owned and/or operated by otherservice providers. For example, the networks 112 may include anothercore network connected to one or more RANs, which may employ the sameRAT as the RAN 103/104/105 and/or RAN 103 b/104 b/105 b or a differentRAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, e.g., theWTRUs 102 a, 102 b, 102 c, 102 d, and 102 e may include multipletransceivers for communicating with different wireless networks overdifferent wireless links. For example, the WTRU 102 e shown in FIG. 4Amay be configured to communicate with the base station 114 a, which mayemploy a cellular-based radio technology, and with the base station 114c, which may employ an IEEE 802 radio technology.

FIG. 4B is a block diagram of an example apparatus or device configuredfor wireless communications in accordance with the embodimentsillustrated herein, such as for example, a WTRU 102. As shown in FIG.4B, the example WTRU 102 may include a processor 118, a transceiver 120,a transmit/receive element 122, a speaker/microphone 124, a keypad 126,a display/touchpad/indicators 128, non-removable memory 130, removablememory 132, a power source 134, a global positioning system (GPS)chipset 136, and other peripherals 138. It will be appreciated that theWTRU 102 may include any sub-combination of the foregoing elements whileremaining consistent with an embodiment. Also, embodiments contemplatethat the base stations 114 a and 114 b, and/or the nodes that basestations 114 a and 114 b may represent, such as but not limited totransceiver station (BTS), a Node-B, a site controller, an access point(AP), a home node-B, an evolved home node-B (eNodeB), a home evolvednode-B (HeNB), a home evolved node-B gateway, and proxy nodes, amongothers, may include some or all of the elements depicted in FIG. 4B anddescribed herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 4Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in an embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In an embodiment, thetransmit/receive Although not shown in FIG. 4A, it will be appreciatedthat the RAN 103/104/105 and/or the core network 106/107/109 may be indirect or indirect communication with other RANs that employ the sameRAT as the RAN 103/104/105 or a different RAT. For example, in additionto being connected to the RAN 103/104/105, which may be utilizing anE-UTRA radio technology, the core network 106/107/109 may also be incommunication with another RAN (not shown) employing a GSM radiotechnology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d to access the PSTN 108, the Internet 110,and/or other networks 112. The PSTN 108 may include circuit-switchedtelephone networks that provide plain old telephone service (POTS). TheInternet 110 may include a global system of interconnected computernetworks and devices that use common communication protocols, such asthe transmission control protocol (TCP), user datagram protocol (UDP)and the internet protocol (IP) in the TCP/IP internet protocol suite.The networks 112 may include wired or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another core network connected to one or moreRANs, which may employ the same RAT as the RAN 103/104/105 or adifferent RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, e.g., theWTRUs 102 a, 102 b, 102 c, and 102 d may include multiple transceiversfor communicating with different wireless networks over differentwireless links. For example, the WTRU 102 c shown in FIG. 4A may beconfigured to communicate with the base station 114 a, which may employa cellular-based radio technology, and with the base station 114 b,which may employ an IEEE 802 radio technology.

FIG. 4B is a block diagram of an example apparatus or device configuredfor wireless communications in accordance with the embodimentsillustrated herein, such as for example, a WTRU 102. As shown in FIG.4B, the example WTRU 102 may include a processor 118, a transceiver 120,a transmit/receive element 122, a speaker/microphone 124, a keypad 126,a display/touchpad/indicators 128, non-removable memory 130, removablememory 132, a power source 134, a global positioning system (GPS)chipset 136, and other peripherals 138. It will be appreciated that theWTRU 102 may include any sub-combination of the foregoing elements whileremaining consistent with an embodiment. Also, embodiments contemplatethat the base stations 114 a and 114 b, and/or the nodes that basestations 114 a and 114 b may represent, such as but not limited totransceiver station (BTS), a Node-B, a site controller, an access point(AP), a home node-B, an evolved home node-B (eNodeB), a home evolvednode-B (HeNB), a home evolved node-B gateway, and proxy nodes, amongothers, may include some or all of the elements depicted in FIG. 4B anddescribed herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 4Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in an embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In an embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet an embodiment, the transmit/receive element 122 may be configuredto transmit and receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 4B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in an embodiment, the WTRU 102 may includetwo or more transmit/receive elements 122 (e.g., multiple antennas) fortransmitting and receiving wireless signals over the air interface115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad/indicators 128 (e.g., a liquid crystal display(LCD) display unit or organic light-emitting diode (OLED) display unit).The processor 118 may also output user data to the speaker/microphone124, the keypad 126, and/or the display/touchpad/indicators 128. Inaddition, the processor 118 may access information from, and store datain, any type of suitable memory, such as the non-removable memory 130and/or the removable memory 132. The non-removable memory 130 mayinclude random-access memory (RAM), read-only memory (ROM), a hard disk,or any other type of memory storage device. The removable memory 132 mayinclude a subscriber identity module (SIM) card, a memory stick, asecure digital (SD) memory card, and the like. In an embodiment, theprocessor 118 may access information from, and store data in, memorythat is not physically located on the WTRU 102, such as on a server or ahome computer (not shown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries, solar cells, fuel cells, and thelike.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include varioussensors such as an accelerometer, biometrics (e.g., finger print)sensors, an e-compass, a satellite transceiver, a digital camera (forphotographs or video), a universal serial bus (USB) port or otherinterconnect interfaces, a vibration device, a television transceiver, ahands free headset, a Bluetooth® module, a frequency modulated (FM)radio unit, a digital music player, a media player, a video game playermodule, an Internet browser, and the like.

The WTRU 102 may be embodied in other apparatuses or devices, such as asensor, consumer electronics, a wearable device such as a smart watch orsmart clothing, a medical or eHealth device, a robot, industrialequipment, a drone, a vehicle such as a car, truck, train, or airplane.The WTRU 102 may connect to other components, modules, or systems ofsuch apparatuses or devices via one or more interconnect interfaces,such as an interconnect interface that may comprise one of theperipherals 138.

FIG. 4C is a system diagram of the RAN 103 and the core network 106according to an embodiment. As noted above, the RAN 103 may employ aUTRA radio technology to communicate with the WTRUs 102 a, 102 b, and102 c over the air interface 115. The RAN 103 may also be incommunication with the core network 106. As shown in FIG. 4C, the RAN103 may include Node-Bs 140 a, 140 b, 140 c, which may each include oneor more transceivers for communicating with the WTRUs 102 a, 102 b, 102c over the air interface 115. The Node-Bs 140 a, 140 b, 140 c may eachbe associated with a particular cell (not shown) within the RAN 103. TheRAN 103 may also include RNCs 142 a, 142 b. It will be appreciated thatthe RAN 103 may include any number of Node-Bs and RNCs while remainingconsistent with an embodiment.

As shown in FIG. 4C, the Node-Bs 140 a, 140 b may be in communicationwith the RNC 142 a. Additionally, the Node-B 140 c may be incommunication with the RNC 142 b. The Node-Bs 140 a, 140 b, 140 c maycommunicate with the respective RNCs 142 a, 142 b via an Iub interface.The RNCs 142 a, 142 b may be in communication with one another via anIur interface. Each of the RNCs 142 a, 142 b may be configured tocontrol the respective Node-Bs 140 a, 140 b, 140 c to which it isconnected. In addition, each of the RNCs 142 a, 142 b may be configuredto carry out or support other functionality, such as outer loop powercontrol, load control, admission control, packet scheduling, handovercontrol, macro-diversity, security functions, data encryption, and thelike.

The core network 106 shown in FIG. 4C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between and the WTRUs102 a, 102 b, 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 4D is a system diagram of the RAN 104 and the core network 107according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, and102 c over the air interface 116. The RAN 104 may also be incommunication with the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In an embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 160 a, 160 b, and 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 4D, theeNode-Bs 160 a, 160 b, 160 c may communicate with one another over an X2interface.

The core network 107 shown in FIG. 4D may include a mobility managementgateway (MME) 162, a serving gateway 164, and a packet data network(PDN) gateway 166. While each of the foregoing elements are depicted aspart of the core network 107, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 162 may be connected to each of the eNode-Bs 160 a, 160 b, and160 c in the RAN 104 via an S1 interface and may serve as a controlnode. For example, the MME 162 may be responsible for authenticatingusers of the WTRUs 102 a, 102 b, 102 c, bearer activation/deactivation,selecting a particular serving gateway during an initial attach of theWTRUs 102 a, 102 b, 102 c, and the like. The MME 162 may also provide acontrol plane function for switching between the RAN 104 and other RANs(not shown) that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNode-Bs 160 a,160 b, and 160 c in the RAN 104 via the S1 interface. The servinggateway 164 may generally route and forward user data packets to/fromthe WTRUs 102 a, 102 b, 102 c. The serving gateway 164 may also performother functions, such as anchoring user planes during inter-eNode Bhandovers, triggering paging when downlink data is available for theWTRUs 102 a, 102 b, 102 c, managing and storing contexts of the WTRUs102 a, 102 b, 102 c, and the like.

The serving gateway 164 may also be connected to the PDN gateway 166,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 107 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 107 and the PSTN 108. In addition, the corenetwork 107 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 4E is a system diagram of the RAN 105 and the core network 109according to an embodiment. The RAN 105 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, and 102 c over the air interface 117. As will befurther discussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 105, andthe core network 109 may be defined as reference points.

As shown in FIG. 4E, the RAN 105 may include base stations 180 a, 180 b,180 c, and an ASN gateway 182, though it will be appreciated that theRAN 105 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 180 a, 180 b,180 c may each be associated with a particular cell in the RAN 105 andmay include one or more transceivers for communicating with the WTRUs102 a, 102 b, 102 c over the air interface 117. In an embodiment, thebase stations 180 a, 180 b, 180 c may implement MIMO technology. Thus,the base station 180 a, for example, may use multiple antennas totransmit wireless signals to, and receive wireless signals from, theWTRU 102 a. The base stations 180 a, 180 b, 180 c may also providemobility management functions, such as handoff triggering, tunnelestablishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 182 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, 102 c and the RAN105 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, and102 c may establish a logical interface (not shown) with the corenetwork 109. The logical interface between the WTRUs 102 a, 102 b, 102 cand the core network 109 may be defined as an R2 reference point, whichmay be used for authentication, authorization, IP host configurationmanagement, and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,and 180 c may be defined as an R8 reference point that includesprotocols for facilitating WTRU handovers and the transfer of databetween base stations. The communication link between the base stations180 a, 180 b, 180 c and the ASN gateway 182 may be defined as an R6reference point. The R6 reference point may include protocols forfacilitating mobility management based on mobility events associatedwith each of the WTRUs 102 a, 102 b, 102 c.

As shown in FIG. 4E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, and 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 184 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 186 may be responsible for userauthentication and for supporting user services. The gateway 188 mayfacilitate interworking with other networks. For example, the gateway188 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 188 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 4E, it will be appreciated that the RAN 105may be connected to other ASNs and the core network 109 may be connectedto other core networks. The communication link between the RAN 105 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 105 and the other ASNs. The communication link betweenthe core network 109 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

The core network entities described herein and illustrated in FIGS. 4A,4C, 4D, and 4E are identified by the names given to those entities incertain existing 3GPP specifications, but it is understood that in thefuture those entities and functionalities may be identified by othernames and certain entities or functions may be combined in futurespecifications published by 3GPP, including future 3GPP NRspecifications. Thus, the particular network entities andfunctionalities described and illustrated in FIGS. 4A, 4B, 4C, 4D, and4E are provided by way of example only, and it is understood that thesubject matter disclosed and claimed herein may be embodied orimplemented in any similar communication system, whether presentlydefined or defined in the future.

FIG. 4F is a block diagram of an exemplary computing system 90 in whichone or more apparatuses of the communications networks illustrated inFIGS. 4A, 4C, 4D and 4E may be embodied, such as certain nodes orfunctional entities in the RAN 103/104/105, Core Network 106/107/109,PSTN 108, Internet 110, or Other Networks 112. Computing system 90 maycomprise a computer or server and may be controlled primarily bycomputer readable instructions, which may be in the form of software,wherever, or by whatever means such software is stored or accessed. Suchcomputer readable instructions may be executed within a processor 91, tocause computing system 90 to do work. The processor 91 may be a generalpurpose processor, a special purpose processor, a conventionalprocessor, a digital signal processor (DSP), a plurality ofmicroprocessors, one or more microprocessors in association with a DSPcore, a controller, a microcontroller, Application Specific IntegratedCircuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, anyother type of integrated circuit (IC), a state machine, and the like.The processor 91 may perform signal coding, data processing, powercontrol, input/output processing, and/or any other functionality thatenables the computing system 90 to operate in a communications network.Coprocessor 81 is an optional processor, distinct from main processor91, that may perform additional functions or assist processor 91.Processor 91 and/or coprocessor 81 may receive, generate, and processdata related to the methods and apparatuses disclosed herein.

In operation, processor 91 fetches, decodes, and executes instructions,and transfers information to and from other resources via the computingsystem's main data-transfer path, system bus 80. Such a system busconnects the components in computing system 90 and defines the mediumfor data exchange. System bus 80 typically includes data lines forsending data, address lines for sending addresses, and control lines forsending interrupts and for operating the system bus. An example of sucha system bus 80 is the PCI (Peripheral Component Interconnect) bus.

Memories coupled to system bus 80 include random access memory (RAM) 82and read only memory (ROM) 93. Such memories include circuitry thatallows information to be stored and retrieved. ROMs 93 generally containstored data that cannot easily be modified. Data stored in RAM 82 can beread or changed by processor 91 or other hardware devices. Access to RAM82 and/or ROM 93 may be controlled by memory controller 92. Memorycontroller 92 may provide an address translation function thattranslates virtual addresses into physical addresses as instructions areexecuted. Memory controller 92 may also provide a memory protectionfunction that isolates processes within the system and isolates systemprocesses from user processes. Thus, a program running in a first modecan access only memory mapped by its own process virtual address space;it cannot access memory within another process's virtual address spaceunless memory sharing between the processes has been set up.

In addition, computing system 90 may contain peripherals controller 83responsible for communicating instructions from processor 91 toperipherals, such as printer 94, keyboard 84, mouse 95, and disk drive85.

Display 86, which is controlled by display controller 96, is used todisplay visual output generated by computing system 90. Such visualoutput may include text, graphics, animated graphics, and video. Thevisual output may be provided in the form of a graphical user interface(GUI). Display 86 may be implemented with a CRT-based video display, anLCD-based flat-panel display, gas plasma-based flat-panel display, or atouch-panel. Display controller 96 includes electronic componentsrequired to generate a video signal that is sent to display 86.

Further, computing system 90 may contain communication circuitry, suchas for example a network adapter 97, that may be used to connectcomputing system 90 to an external communications network, such as theRAN 103/104/105, Core Network 106/107/109, PSTN 108, Internet 110, orOther Networks 112 of FIGS. 4A, 4B, 4C, 4D, and 4E, to enable thecomputing system 90 to communicate with other nodes or functionalentities of those networks. The communication circuitry, alone or incombination with the processor 91, may be used to perform thetransmitting and receiving steps of certain apparatuses, nodes, orfunctional entities described herein.

It is understood that any or all of the apparatuses, systems, methodsand processes described herein may be embodied in the form of computerexecutable instructions (e.g., program code) stored on acomputer-readable storage medium which instructions, when executed by aprocessor, such as processors 118 or 91, cause the processor to performand/or implement the systems, methods and processes described herein.Specifically, any of the steps, operations or functions described hereinmay be implemented in the form of such computer executable instructions,executing on the processor of an apparatus or computing systemconfigured for wireless and/or wired network communications. Computerreadable storage media include volatile and nonvolatile, removable andnon-removable media implemented in any non-transitory (e.g., tangible orphysical) method or technology for storage of information, but suchcomputer readable storage media do not includes signals. Computerreadable storage media include, but are not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other tangible or physical medium which can be used to store thedesired information and which can be accessed by a computing system.

The following is a list of acronyms relating to service leveltechnologies that may appear in the above description. Unless otherwisespecified, the acronyms used herein refer to the corresponding termlisted below.

AAS Active Antenna System

AoA Angle or Arrival

AoD Angle of Departure

AS Access Stratum

CE Control Element

CoMP Coordinated Multipoint

CP Cyclic Prefix

CQI Channel Quality Indication

CRS Cell-specific Reference Signals

CSI Channel State Information

CSI-RS Channel State Information Reference Signals

DCI Downlink Control Information

DL DownLink

DM-RS Demodulation Reference Signals

eMBB enhanced Mobile Broadband

eNB evolved Node B

ePDCCH Enhanced Physical Downlink Control CHannel

FD Full-Dimension

FDD Frequency Division Duplex

FFS For Further Study

GUI Graphical User Interface

HARQ Hybrid Automatic Repeat Request

ID Identification

IMT International Mobile Telecommunications

KP Kronecker-Product

KPI Key Performance Indicators

LTE Long term Evolution

MCL Maximum Coupling Loss

MCS Modulation and Coding Scheme

MME Mobility Management Entity

MIMO Multiple-Input and Multiple-Output

NAS Non-Access Stratumn

NB Narrow Beam

NDI New Data Indicator

NEO NEtwork Operation

OCC Orthogonal Cover Codes

OFDM Orthogonal Frequency Division Multiplexing

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PMI Precoder Matrix Indication

PRS Positioning Reference Signals

PUSCH Physical Uplink Shared Channel

PUCCH Physical Uplink Control Channel

RB Resource Block

RE Resource Element

RI Rank Indication

RRC Radio Resource Control

RS Reference Signal

RSSI Received Signal Strength Indicator

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

RV Redundancy Version

SISO Single-Input and Single-Output

SRS Sounding Reference Signal

2D Two-Dimensional

3D Three-Dimensional

TDD Time Division Duplex

TPC Transmit Power Control

TRP Transmission and Reception Point

UE User Equipment

UL UpLink

URLLC Ultra-Reliable and Low Latency Communications

WB Wide Beam

WRC Wireless Planning Coordination

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed:
 1. An apparatus comprising a processor, a memory, andcommunication circuitry, the apparatus being connected to a network viaits communication circuitry, the apparatus further comprisingcomputer-executable instructions stored in the memory of the apparatuswhich, when executed by the processor of the apparatus, cause theapparatus to perform operations comprising: receiving, via RadioResource Control (RRC) signaling, a Channel State Information (CSI)report configuration indicating a feedback type for a CSI referencesignal, the CSI report configuration being associated with one or morebeam indexes; selecting one or more beams from a plurality of beamsprovided by at least one node in the network; sending, to the at leastone node, a beam index feedback with a CSI report that indicates theselected one or more beams based on the CSI report configuration;receiving, until a beam is reselected, a CSI reference signal anddownlink (DL) data via the selected one or more beams; and sending abeam re-selection request, via a Physical Uplink Control CHannel(PUCCH), to the at least one node, wherein the beam re-selection requestcomprises a first bit that indicates that the beam should bere-selected.
 2. The apparatus of claim 1, wherein the plurality of beamsare provided by a plurality of nodes in the network, and the apparatusfurther comprises computer-executable instructions stored in the memoryof the apparatus which, when executed by the processor of the apparatus,cause the apparatus to perform further operations comprising: detectingthe plurality of beams from the plurality of nodes; and sending, to theplurality of nodes, an index associated with each node that isassociated with at least one of the one or more selected beams.
 3. Theapparatus of claim 1, wherein the CSI report comprises a respectiveindex associated with a preconfigured number of beams.
 4. The apparatusof claim 1, wherein the beam is re-selected in accordance with apreconfigured periodicity.
 5. The apparatus of claim 1, wherein the CSIreport is sent to the at least one node periodically.
 6. The apparatusof claim 1, wherein the CSI report is sent to the at least one nodeaperiodically.
 7. The apparatus of the claim 1, wherein the CSI reportis sent for beams configured by a higher layer.
 8. The apparatus ofclaim 1, wherein the beam re-selection request further comprises asecond bit that indicates whether the beam should be re-selected using anew beam sweep.
 9. An apparatus comprising a processor, a memory, andcommunication circuitry, the apparatus being connected to a network viaits communication circuitry, the apparatus further comprisingcomputer-executable instructions stored in the memory of the apparatuswhich, when executed by the processor of the apparatus, cause theapparatus to perform operations comprising: receiving, from a node onthe network, a Channel State Information Reference Signal (CSI-RS)associated with a channel estimation; based on the channel estimation,selecting one or more antenna ports from a plurality of antenna ports;sending, to the node, an antenna port index report that indicates theselected one or more antenna ports, the antenna port index pertaining toa beam; receiving, until an antenna port is reselected, the CSI-RS viathe selected one or more antenna ports; and sending a beam re-selectionrequest, via an uplink control channel, to the at least one node, thebeam re-selection request comprising an indication of whether a beamreselection begins at a beam sweep stage or beamforming training. 10.The apparatus of claim 9, wherein the one or more antenna ports areselected based on predetermined criteria.
 11. The apparatus of claim 9,wherein the CSI-RS is received periodically.
 12. The apparatus of claim9, wherein the instructions cause the apparatus to perform furtheroperations comprising: sending a request for the CSI-RS, so as totrigger the CSI-RS, such that the CSI-RS is received aperiodically. 13.The apparatus of claim 9, wherein the selected one or more antenna portscorresponds to a predetermined fixed number of antenna ports, and theapparatus further comprises computer-executable instructions stored inthe memory of the apparatus which, when executed by the processor of theapparatus, cause the apparatus to perform further operations comprising:receiving, from the node, an indication of a minimum number of antennaports that the apparatus is required to support, and an indication of amaximum number of antenna ports that are permitted to be selected,wherein the selected one or more antenna ports total a number at leastequal to the minimum number and no greater than the maximum number. 14.The apparatus of claim 9, wherein the selected one or more antenna portsare indicated using a bit map.
 15. The apparatus of claim 9, wherein theselected one or more antenna ports are indicated using a logarithmic bitbinary sequence.
 16. The apparatus of claim 9, wherein the antenna portindex report is partitioned into groups of antenna ports, such that onlyone antenna port can be selected from each group.
 17. The apparatus ofclaim 9, wherein the beam re-selection request is sent using a highreliability channel coding.
 18. The apparatus of claim 9, wherein thebeam re-selection is configured by higher layer signaling using RadioResource Control (RRC) signaling or a Medium Access Control—ControlElement (MAC CE).
 19. The apparatus of claim 9, wherein the beamre-selection request is fed back jointly to a plurality of Transmissionand Reception Point (TRPs).
 20. A network node comprising a processor, amemory, and communication circuitry, the apparatus being connected to anetwork via its communication circuitry, the apparatus furthercomprising computer-executable instructions stored in the memory of theapparatus which, when executed by the processor of the apparatus, causethe apparatus to perform operations comprising: transmitting, via RadioResource Control (RRC) signaling, a Channel State Information (CSI)report configuration indicating a feedback type for a CSI referencesignal, the CSI report configuration being associated with one or morebeam indexes; receiving, from a user device, a beam index feedback witha CSI report that indicates one or more beams selected by the userdevice based on the CSI report configuration; transmitting a channelstate information CSI reference signal and downlink (DL) data via theone or more beams; and receiving a beam re-selection request, via aPhysical Uplink Control CHannel (PUCCH), from the user device, whereinthe beam re-selection request comprises a first bit that indicates thatthe beam should be re-selected.